Why the Past Does not Wait for Us
The
grandfather paradox
is
a well-known problem of a time travel. According to this paradox, a
time traveller goes back in time and kills his grandfather before he
even meets his grandmother. As a result of this, the time traveller
can never be born. However, if he was never born, then he is not able
to travel through time and kill his grandfather, which subsequently
means that the traveller would be born after all.
We
must realise that a totally necessary precondition to this paradox is
that the past remains absolutely unchanged forever, waiting for our
time traveller. Therefore, the almost 14 billion-year history of the
whole universe must be stored somewhere and being fixed up to a
quantum level. What is more,
this
past must
exist
without
any smallest change and be fully flexible at the same time, reacting
to the actions of time travellers. Nothing else but our time
traveller can change it, so it is almost a "personal"
world, and this indicates that such past is only in our fantasy.
If
a time traveller could not change history, meaning he could not
interact with his surroundings in the past, it would not be time
travelling in
the usual sense of the term.
This would be a mere historic 3D "movie". So, should time
travel be possible, we ought
to consider
a changeable past. If it is changeable, the past will look (very)
different when reached by the time traveller. Hence, the past is
currently not what it used to be when we were there. (In an extreme
case, there would be no past to return to.)
Speaking
metaphorically, let us imagine that the time traveller is a fish born
from a fish egg in a mountain river, carried away to a valley. He can
later swim back up to the mountains to the exact place of his birth,
but he will not find the fish egg from which he was born, neither his
mother delivering the egg. Moreover, we can even imagine that the
mountains are very dry, without any water source, and he was born
during a flood wave. Should the time traveller return back, he will
not find anything remotely similar to his original water world.
Now
let me offer you a more advanced visual metaphor inspired by the 4D
Minkowski space-time model as well as
some
cosmological models. Our 3D universe is a 3D hyper-surface
of a 4D hyper-bubble which expands. This expansion is time. For a
better understanding, we can go by one dimension lower and picture
only a 3D bubble with a 2D surface. Now we can imagine that the
bubble is full of "liquid" which the surface is composed of
as well, or alternatively there is only a surface membrane and the
bubble is empty. There is also a third possibility: there are only
parts of the past inside the bubble, some drops or trickles or
similar. In all cases, the past is either dynamic or non-existent,
but never static and
unchanged.
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(Source: http://www.awesomenator.com/) |
I
personally prefer the empty bubble, which is a result of the fact
that we cannot see the past from our presence, so it looks like we
live inside a 3D hyper-membrane
only. Of course, a concrete physical mechanism of our time must be
discovered and proved by physics.
I certainly
do not insist on the 4D bubble or any particular solution. Although,
the 4D Minkowski space-time model with its specific hyperbolic
attributes offers us a good clue. Instead, I am merely suggesting
that there are solutions which remove the grandfather paradox and all
time travel paradoxes, and these solutions contain changes to
the
past or even physical non-existence of the past. The question whether
the dynamics of the past is very slow, immediate and disappearing, or
like a wave after a boat, is an area for further investigation of
natural sciences.
Because
the case of the empty bubble seems to be simple, we will investigate
further the bubble full of "liquid", which is in fact
"liquid of past". One possibility is that the time
traveller would not meet his grandfather, because the granddad would
have disappeared and would not be there anymore. But if he was still
there, the death of the granddad (by the hand of the time traveller)
and its consequences would be delayed behind the actual
position/motion of the 3D surface, never reaching it because the
velocity of the impacts would be the same as the velocity of the 3D
surface. (The velocity of the light cone movement alongside the time
axis is c
within the Minkowski space-time model, and mutual velocity of two
objects with c
velocity is again
c.)
Returning back to the original time, the time traveller would not see
any consequences of his action and would not notice any changes to
history. Our time would not wait for impacts of changed history, and
would simply move farther. By
the way, the traveller would not be able to go back to that original
moment of time, from which he departed.
Furthermore,
in the case of "full bubble", there will not be any 3D time
membrane; there will be only a 4D hyper-space
which we cannot see by light rays. (We know this from our 3D world
where we cannot see 4D space.) Hence, being in history, we would not
observe any world similar to ours, and our way of interaction with
surroundings would be very physically different. We would not be able
to see the history (via light), to touch objects there, neither we
would be able to speak to people who in fact would not be people like
in our world.
Therefore,
in this bubble model, there is no way of considering time travelling
precisely
in a traditional meaning of the term.
Let me offer you one possibility a bit similar to the conventional
understanding of the term. Imagine, that we can dent the bubble and
move a local part of the membrane to the past or to the future. It
would be something different than a common extraction of the time
traveller from our time. Instead, it would be a local continuous
deformation of our space-time where the time traveller goes back in
time together with us and the entire environment. In this case, the
grandfather paradox is out of the question and practically
impossible. When the time goes back before our birth, there could be
our granddad, but certainly not us. And
so, the causality that would otherwise be
heavily
damaged
by
the grandfather paradox,
is saved.
There
is one very probable conclusion resulting from this thinking:
Considering our time as a motion of our universe (3D hyper-surface),
we are looking at it from a hyper-space
and
thinking in hyper-time. In this case, we
perceive
our time only as one motion in hyper-time. Based
on the assumption of the hyper-time,
there is no problem regarding the beginning of our time in the big
bang as a creation of our universe from the multiverse. Hyper-time
would be the time of multiverse. This would also explain the origin
of time relativity.
Ultimately,
the grandfather paradox does not suggest that time travelling is
impossible, however, it shows us what kind of time travelling is
impossible (fixed waiting past). Therefore, it offers us detailed
information on how the
nature of time
travel should look like.